Spermatogenesis is a complex process of cell differentiation involving interactions between germ cells. Sertoli cells, and other somatic cells within the testis. One feature of this process is the appearance of several germ cell-specific constituents in a precise temporal sequence. Three areas of research have been pursued to further characterize these unique constituents, both in the acrosome and on the cell surface. (a) Monoclonal antibodies have been used to identify and characterize germ cell components expressed during restricted periods of spermatogenesis. Antibody 104 reacts with multiple glycoconjugates that appear in the acrosome of early spermatids but are modified during the late haploid stages so that the determinant is no longer detected. In contrast, this antibody recognizes acrosomal glycoconjugates that are retained in guinea pig spermatozoa. Additional monoclonal antibodies that recognize cell surface constituents with stage-and tissue-specificity have been prepared against proteins excised from two-dimensional gels. (b) The two mannose 6-phosphate (M6P) receptors, which may have roles in intercellular communication and in targeting hydrolases to the acrosome, are synthesized in distinct proportions in pachytene spermatocytes round spermatids, and Sertoli cells. We have shown that these cell types have functional M6P receptors on their cell surfaces and that Sertoli cells secrets M6P-bearing glycoproteins. (c) Interactions between Sertoli cells and germ cells at defined stages of spermatogenesis have been examined in short-term cultures. When cultured in the presence of Sertoli cell- conditioned medium (SCM), pachytene spermatocytes and round spermatids maintain elevated viabilities and ATP levels. SCM contains multiple glycoproteins and its active fraction has stability characteristics that distinguish it from Sertoli cell growth factors described previously. Germ cell and sertoli cell constituents, particularly those exhibiting stage and tissue specificity, are candidates for further studies exploring gene regulation and cell interactions during spermatogenesis.